The Stovebolt Site Forums The Shop Area General Truck Talk Down on power

general question for the engine-minded readers out there.

The motor in my chevy feels down on power. Its starts ok, has new points, plugs leads, rotor arm, cap and condenser. The settings (where applicable) are all correct, having just checked them. The carb has been cleaned, and at a standstill, in neutral, she runs up fine.
Under load, it feels stiffled. Not sluggish, but as though it's being held back. It's hard to describe in words, but very noticable when your driving (which it does, but very slowly)
Leaving aside the fact it's a 235 chevy six, and it's never going to be a tarmac-scorcher, the ability to escape from tail-gating hgv's would be nice! Oh, and don't ask me about hill starts....

Any suggestions would be greatly accepted, please assume total mechanical ignorance (your talking to an ex-diesel fitter!!)

Thanks in advance

Taff

Taff,

How about the fuel system? A plugged fuel system might cause some of the conditions you describe. I am not sure what type of vehicle you are running your 235 in but if the tank is old, you might have some sediment clogging up the works. The fuel filter might be clogged. If no fuel filter, maybe a chunk of dirt where it does not belong?

Sounds like the timing is retarded. Did it do this before the tuneup?Possibly a resriction in the exhaust system.

Taff,

What are you comparing the rig to when you say it is stifled. Usually if the engine starts, runs well and doesn't burn oil and smoke, it's a clean bill of health!

This would mean it's a tuning issue. Timing is very critical for the proper get up and go! The carburetor has a power valve in it that gives the engine a shot of caffeine when you put your foot in it.

If it isn't some mechanical issue, such as dragging brakes, then it must be in the power production end of the equation.

You haven't indicated what kind of rig you have. Is it a standard transmission or automatic? One of the first steps would be to take a compression reading so you can get a handle on what you are dealing with.

I would verify the timing again. Vacuum is critical...no leaks are allowed. The vacuum advance on the distributor must function and the gasket under the carburetor must be positioned to allow the carburetor to sense manifold vacuum.

Take a look at your exhaust system too! Maybe someone put a potatoe in your pipe.

To get net, if the engine is in good condition, then you have a tuning issue. If the engine isn't in good condition then that's the problem.

Stuart

Also try a compression check. Weak cylinder will result in lack of power, especially in something that lacks power anyway. Sorry, I guess I'm just used to my vette powertrain.

Sounds like timing to me. Re-check your point gap/dwell because new points wear in quickly and need to be re-set during break-in because the rubbing block will change quickly at first. Double check your timing, with vacuum spark advance line disconnected and plugged. Sometimes, they'll run better with more initial advance than the book calls for, so it can be a little of the trial and error method until it starts running good. Also, put a little vacuum on your vacuum advance cannister and see if the points advance (this is more for fuel economy than for performance).

Retarded timing will idle nice and smooth but won't power itself out of a wet paper bag.

Guy's, thanks for the advice. Like I said, I was a diesel fitter for a long time, so I'm used to fuel/air/compression and thats all you need.....LOL
To answer a few of the questions, the tank is new, as is the line and the fuel filter.
The exhaust is ok, not bloked, but the "flutter" valve in the exhaust manifold is a little stiff, so I will strip and free this off later.
The trans is a stock 3-on-the-tree.I will re0set the points, it was on my list of "to do", as I knew they would wear quite a lot initially.

General consensus points towards check and double check the timing, I'll run thru' that first thing and report back.
Thanks for the advice dude's, very much appreciatted.
Taff

I'm with WALDO53, I would have the vacuum advance checked. Many of the older distributors had adjustable advance canisters. Also the advance plate it's self may be frozen It may idle decent but not advancing the spark under load.

It would be more likely an initial advance problem than a vacuum advance problem in this case. There is little vacuum advance at load anyway, as its purpose is to add advance at low throttle openings to improve milage.

Just been out for a look at the motor, at the risk of sounding stupid where are the ignition timing marks? Is there something to be seen through the whole in the belhousing?

Taff,

Jolly good...you've found them. The 'hole' in question is the one above the starter. There is a pointer attached to the top of the casting/hole. There is a BB or similar item marked or embedded in the flywheel. The proper timing is achieved with a timing light and the alignment of the BB and the pointer when the strobe flashes.

More folks will add the details for sure!

Stuart

Hi all
Thought I would put an update on, as everyone was so helpful.
I pulled the valve cover off this morning, set No1 to tdc, pull out the dizzy and put it back in the right place, turned the key and she fired up and ran beautifully! And on the move, the car is transformed!! No over-heating, sips the fuel, pulls strong in every gear.

Thanks once again for all your help and advice
Cheers, Taff

Good job Taff!! Guess this means you won't have any more problems with those tailgating #$&&*'s!!

Waldo. you know what? I hate ignition timing as well, was a diesel and plant fitter for too long.........but she's running so sweet now, just gone round the block in her again.
Oh, and as for the truck drivers, they can go sniff my tailpipe!!